Where did the left-hand toolbar go?
You changed to Object or Edit mode as you said, the combobox(button) where you can change to Object or Edit mode also offers the option for Sculpting Mode.

While the option to change to Sculpting mode is only available if an object that can be sculpted on is selected,(no camera, light, empty, etc..) that is to say generally only mesh objects can be sculpted on.

Here a little video showing the change to Sculpt mode:



Happy Blending.